The King's Fund is to invest £1m a year in a grant-making scheme called Partners for Health in London, which has been designed to tackle unmet health needs.
Developing mental health advocacy, promoting better sexual health and improving end-of-life care are the three areas covered by the new grants programme, which is open to London-based charities with an income of more than £150,000.
Funding will be allocated to organisations for services in these areas and for research into how well the services are working or how they can be improved. The fund expects to play an integral role in research and will work closely with the organisations.
Kings Fund chief executive Niall Dickson said: "This is not just about funding a few projects in London - it is about learning in practice and spreading what we have learnt."
Partners for Health in London awards will range from £5,000 to a maximum of £150,000 for up to three years, with the first round of applications due to be accepted this autumn.
The mental health grant stream is aimed at organisations working to develop and deliver services that can help to establish how effective mental health advocates might be.